Ulcers occurring in the stomach or duodenum are caused primarily by hypersecretion of gastric acid. Some drugs are known recently for inhibiting the secretion of gastric acid by blocking the activity of the histamine H.sub.2 receptor. Several kinds of drugs of this class, such as cimetidine and famotidine, are commercially available at present. However, although these histamine H.sub.2 receptor antagonists exhibit high curing effects, they have the problem of being very likely to permit subsequent recurrence, so that it has been attempted to use such antagonists in combination with an anti-ulcer drug having activity to protect the gastric mucosa. Accordingly, drugs for treating peptic ulcers should preferably have activity to inhibit gastric acid secretion and activity to protect the gastric mucosa, and it is strongly desired to develop drugs having both of these activities.